Sloths Can Hold Their Breath

While famous for their sluggish pace in the trees, three-toed sloths reveal an unexpected athletic talent in the water (Review). Living in the frequently flooded rainforests of Central and South America, they often use rivers and waterways as convenient highways. To travel to a new patch of trees or find a mate, a sloth will simply let go of a branch and plunge into the water below. They are surprisingly powerful swimmers, paddling through the water with their long arms at a pace that is about three times faster than they can crawl across the forest floor.

This aquatic ability is supported by an incredible physiological adaptation. A sloth can submerge itself for an astonishing 40 minutes by intentionally slowing its heart rate to less than a third of its normal pace. This dramatic reduction in heartbeats, combined with their already famously slow metabolism, means their bodies use a tiny fraction of the oxygen a typical mammal would. This extreme energy conservation allows them to perform these long, underwater journeys without needing to surface for air, turning their greatest weakness on land—slowness—into a unique underwater strength.